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A new report is making waves in the world of climate science as it’s pinpointed how extreme weather events of 2013 are linked to global warming. The American Meteorological Society’s bulletin looked at 22 different studies and found that the record-setting temperatures in places like Australia made heat waves both more intense and more likely. And they’re pointing the finger at the emission of greenhouse gases as causing these extreme weather events.

With us to help break down the report and the link between climate change and the extreme weather events is Jeff Masters. Jeff is a meteorologist and the director of meteorology for WeatherUnderground.com. And he joins us now from Ann Arbor, Michigan.

DESVARIEUX: So, Jeff, let’s take a look at this report. And can you just break down for us which extreme events of 2013 were judged to be significantly influenced by climate change and which were not?

MASTERS: The heat waves were the events that were most likely to be influenced by climate change. In particular, in Australia they had their hottest year on record last year, and a few hottest months on record as well, and five of the studies found convincing evidence that human-caused climate change was to blame for those extremes. Also, heat waves in Korea, Japan, China, and Western Europe were also judged to be due to climate change in a large sense.

Now, for precipitation extremes, the jury was out on the influence of human-caused climate change. For instance, the Colorado floods, some rainstorms in Europe, and a couple of blizzards, a South Dakota blizzard and a European winter storm, the influence of climate change was thought maybe to be there, but it was hard to tell with the natural sorts of ups and downs that the weather and climate have.

DESVARIEUX: Jeff, I want to take a closer look at the evidence that you mention. How did the researchers arrived to their conclusions?

MASTERS: What they do is they run climate models, which are these computer models that divide up the atmosphere into little grid cells, and they solve the equations of mathematical theory that show how the atmosphere should behave on each one of those little grid cells going through time with the expected concentrations of heat-trapping gases like carbon dioxide. What you can do is you can run it with the atmosphere we expected to exist 100 years ago, I mean, before we started putting so much CO2 in the air, and then now and compare the two results. And in particular, I mean, the planet has warmed by about a degree Fahrenheit in that time. You can see what that 1 degree Fahrenheit kind of background warming has done to the atmosphere, and to extreme events in particular.

DESVARIEUX: Something that caught my attention when I looked at the report is that the National Climate Assessment made a connection between climate change and drought in Australia, but it didn’t do it for the ongoing California drought. Why didn’t they make that connection?

MASTERS: Yeah, it’s interesting. I mean, the drought in Australia and in New Zealand, both the climate models that they ran for those events did show a pretty clear signal. But it’s interesting. For the California drought, they did three studies in this particular work, and two of the three said, well, we can’t tell whether natural variability might have been masking the effects of human-caused climate change. The third study did show that human-caused climate change was to blame.

Now, the two that didn’t find human-caused climate change involved, they left out some very important influences, like the fact that Arctic Sea ice has been going down, the fact that soils have been trying out. When soils dry out they tend to heat up the atmosphere more and drive more intense droughts. So we can criticize mythology in some of these studies. They were not complete studies. They left out some very important impacts. So they were limited. They can show with of their limitations that such and such an event was more likely or not to occur, but they didn’t include everything.

DESVARIEUX: But, Jeff, at the conclusion of the report–I want to bring this up because a lot of people are probably going to probably make this counterargument–it mentioned that it’s hard to say for certain that some extreme weather events were caused by climate change, but scientists are pretty confident about the connection in other cases. Does that raise any doubts in your mind that the two are related?

MASTERS: It’s not so hard in the case of heat to say that human-caused climate change is to blame. I mean, we’re heating up the planet. And, yeah, it’s pretty obvious that you’re going to have more increased heat extremes in a warmer climate. Now, with heavy precipitation events it’s a little more complicated, because, yeah, when you heat up the oceans, you’re driving more evaporation, putting more moisture in the air, which can theoretically cause more intense heavy rainfall events. But there’s other things going on as well. You’re changing the very background nature within which storms form. You’re taking the jet stream, the path along which these storms travel. So it gets pretty complicated, and you can’t say with as great a certainty that these events are due to human-caused climate change.

DESVARIEUX: Okay. There was also something interesting, this new science of extreme event attribution. First of all, what is it? And how reliable is it in determining that there’s a connection?

MASTERS: Simply, extreme event attribution is you’re assigning a probability that a particular weather event was due to human-caused climate change or made more likely due to human-caused climate change. In particular, for instance, the heatwave in Korea they said was ten times more likely due to human-caused climate change than if we hadn’t warmed up our planet.

And this is very new research. It’s very breaking sort of–we’re experimenting around trying to figure this stuff out. We don’t have all the answers to this sort of research. It’s very much experimental. And we should just look at it is kind of a early attempt to figure out what’s going on. And it’s going to get better through time.

DESVARIEUX: Yeah, and what I’ve seen is sort of change is how vocal climate scientists have been about linking weather events to climate change, because in the past they were were very hesitant, but we’re seeing more examples of this happen, like with this study and others. What do you think is influencing this shift?

MASTERS: Our computer models are getting more powerful. I mean, as computers double in power every year and a half, we’re able to drive better and better models of the atmosphere, subdivide it into grids that are even finer and finer and put more time steps into them. So we’re just getting a better sort of tool to analyze things, and our understanding is growing as well.

End

Related Bios

Dr. Jeff Masters has been a meteorologist for 33 years. He flew with the NOAA Hurricane Hunters from 1986 – 1991, and earned his Ph.D. in air pollution meteorology in 1997 from the University of Michigan. He co-founded the Weather Underground, Inc. in 1995, and served on its board of directors until the company was…

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